1. Field of the Invention
The present invention relates to a memory component and a memory device capable of storing information using a change in electrical characteristics of a memory layer that includes an ion source layer and a resistance variable layer, and a method of operating a memory device.
2. Description of the Related Art
In information equipment such as a computer, high-speed and high-density DRAMs (Dynamic Random Access Memory) have been widely used as a random access memory. However, DRAMs involve high manufacturing costs due to their complicated manufacturing process as compared to typical logic circuit LSIs and signal processing circuits used in electronic equipment. Moreover, DRAMs are volatile memories in which information is lost when power is turned off. Therefore, it is necessary for DRAMs to perform a frequent refresh operation; that is, the written information (data) must be read, amplified again and rewritten.
In the related art, for example, flash memories, FeRAMs (Ferroelectric Random Access Memories; ferroelectric memories), MRAMs (Magnetoresistive Random Access Memories; magnetic memory components), and the like have been proposed as nonvolatile memories which can retain information even when power is turned off. These memories can retain the written information for an extended period even when no power is supplied. However, these memories have their advantages and disadvantages. That is, flash memories have a high degree of integration but are disadvantageous in terms of operating speed. FeRAMs have limitations in micro-patterning required for higher degrees of integration and also have problems with their manufacturing process. MRAMs have problems with their power consumption.
Therefore, a new type of memory component is proposed which is particularly advantageous in overcoming the limitations in micro-patterning memory components. This memory component has a structure in which an ion conductor containing a certain metal is sandwiched between two electrodes. In this memory component, the metal contained in the ion conductor is contained in anyone of the two electrodes. As a result, when a voltage is applied between the two electrodes, the metal contained in the electrode diffuses into the ion conductor as ions. Thus, electrical characteristics, such as a resistance value or a capacitance, of the ion conductor are changed. For example, JP-T-2002-536840 proposes an example of a memory device using this property. The memory device proposed in JP-T-2002-536840 has a configuration in which the ion conductor is made of a solid solution of chalcogenide and metal. Specifically, the ion conductor is made of a material in which Ag, Cu or Zn is dissolved in AsS, GeS, and GeSe, and Ag, Cu, or Zn is contained in any one of the two electrodes.
In the configuration disclosed in JP-T-2002-536840, due to a temperature rise during the manufacturing process or a long-term thermal load when data is retained for an extended period, crystallization of the ion conductor is accelerated, and the original electrical characteristics such as a resistance value are changed. Therefore, JP-A-2005-197634 proposes a configuration in which a thin memory film made of a gadolinium oxide film is provided between the ion conductor and the electrode.